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Journal of Experimental and Theoretical Physics Letters

Effect of coulomb correlations on the two-level quantum dot susceptibility and polarization

N. S. Maslova, Vladimir N. Mantsevich, P. I. Arseyev

Published Oct 1, 2015• 0 citations
Publisher

Abstract

We revealed that the susceptibility and polarization of two-level quantum dot (QD) with Coulomb correlations between localized electrons weakly connected to the reservoirs are determined not only by the stationary electron filling numbers difference. We demonstrated that the susceptibility and polarization also depend on high-order correlation functions of electrons localized in the QD. We found that susceptibility and polarization can be controlled by applied bias voltage value, Coulomb correlations strength and Rabi frequency. We demonstrated that susceptibility and polarization amplitudes can significantly increase and even change the sign due to the tuning of the QD parameters. Careful analysis of correlated QD susceptibility, polarization and electron filling numbers (occupancies) difference in a wide range of applied bias voltage, Rabi frequency and Coulomb correlations value was performed in terms of pseudo-operators with constraint.

DOI
10.1134/s0021364015200096

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We revealed that the susceptibility and polarization of two-level quantum dot (QD) with Coulomb correlations between localized electrons weakly connected to the reservoirs are determined not only by the stationary electron filling numbers difference. We demonstrated that the susceptibility and polarization also depend on high-order correlation functions of electrons localized in the QD. We found that susceptibility and polarization can be controlled by applied bias voltage value, Coulomb correlations strength and Rabi frequency. We demonstrated that susceptibility and polarization amplitudes can significantly increase and even change the sign due to the tuning of the QD parameters. Careful analysis of correlated QD susceptibility, polarization and electron filling numbers (occupancies) difference in a wide range of applied bias voltage, Rabi frequency and Coulomb correlations value was performed in terms of pseudo-operators with constraint.
We study the relaxation dynamics of a quantum dot with local Coulomb correlations coupled to two noninteracting leads which are held in grand-canonical equilibrium. Only charge degrees of freedom are considered and the dot is described by a model which in the scaling limit becomes equivalent to the interacting resonant level model. We examine the time evolution of the current and the dot occupancy resulting from changes in the dot-lead coupling, the dots' on-site energy, or the charging energy. Abrupt and smooth parameter changes as well as setups with and without driving bias voltage are considered. For biased dots, we investigate the often studied response after turning on the dot-lead coupling but also the experimentally more relevant case in which the voltage is turned on. We identify and explain a variety of interesting many-body effects, and we clarify the role of initial correlations.
Double quantum dots are one of the promising two-state quantum systems for realizing qubits. In the quest of successfully manipulating and reading information in qubit systems, it is of prime interest to control the charge response of the system to a gate voltage, as filled in by the dynamical charge susceptibility. We theoretically study this quantity for a nonequilibrium double quantum dot by using the functional integral approach and derive its general analytical expression. One highlights the existence of two lines of maxima as a function of the dot level energies, each of them being split under the action of a bias voltage. In the low frequency limit, we derive the capacitance and the charge relaxation resistance of the equivalent quantum RC-circuit with a notable difference in the range of variation for RRR depending on whether the system is connected in series or in parallel. By incorporating an additional triplet state in order to describe the situation of a double quantum dot with spin, we obtain results for the resonator phase response which are in qualitative agreement with recent experimental observations in spin qubit systems. These results show the wealth of information brought by the knowledge of dynamical charge susceptibility in double quantum dots with potential applications for spin qubits.
An all electrical manipulation with singlet and triplet states of an electron pair in a quadruple quantum dot (QD) has been studied by a configuration interaction method. We have investigated two nanodevices that consist of four weakly coupled lateral QDs, in which the electron localization can be changed by tuning the external voltages: the gate voltage in the first nanodevice and the source-drain voltage in the second. The electrons that---in the initial state---singly occupy the two identical input QDs are transferred to the two asymmetric output QDs by the sufficiently high electric field. We have shown that---for the QDs with suitably chosen parameters---the localization of the electrons in the output QDs depends on the spin states of the electron pair and the final spin state can be uniquely determined by a single-shot measurement of the electric charge gathered in only one of the output QDs. This leads to a possibility of performing the controlled operations on the electron-spin qubits in the quadruple QDs. We have found that the classical exclusive OR (XOR) logic gate can be performed with the electric field-induced transitions and the output read out by the spin-to-charge conversion.
Using a real-time renormalization group method we study the minimal model of a quantum dot dominated by charge fluctuations, the two-lead interacting resonant level model, at finite bias voltage. We develop a set of RG equations to treat the case of weak and strong charge fluctuations, together with the determination of power-law exponents up to second order in the Coulomb interaction. We derive analytic expressions for the charge susceptibility, the steady-state current, and the conductance in the situation of arbitrary system parameters, in particular away from the particle-hole symmetric point and for asymmetric Coulomb interactions. In the asymmetric situation we find that power laws can be observed for the current only as a function of the level position (gate voltage) but in general not as a function of the voltage except for extremely large voltages. Furthermore, we study the quench dynamics after sudden switch-on of the level-lead couplings. The time evolution of the dot occupation and current is governed by exponential relaxation accompanied by voltage-dependent oscillations and characteristic algebraic decay.
The influence of electron-hole dipole-dipole interactions (local fields) on the excitonic Rabi oscillations in an isolated quantum dot (QD) has been theoretically investigated. An analysis for the QD interaction with monochromatic field and ultrashort Gaussian pulse has been performed. On the basis of optical Bloch equations the Rabi oscillation dynamics has been investigated. As a result, the bifurcation and essentially anharmonic regimes in the Rabi oscillations in a QD exposed to the monochromatic field have been predicted. The strong dependence of the period of Rabi oscillations on the QD depolarization has been revealed. For the Gaussian pulse it has been shown that the final state of inversion as a function of the pulse peak strength demonstrates step-like transitions.